Production of desulfurized gasoline



Patented Nov. 21, 1950 UNITED STATES PATENT OFFICE 2,530,701 PRODUCTION or DESULFURIZED GASOLINE Delaware Application June 15, 1948, Serial N 0. 33,098

- This invention relates to the production of mercaptan free gasoline from sulfur-containing petroleum oils through catalytic cracking.

I Allcrude petroleums contain at least some sulfur. However, the sulfur contents vary with petroleums from different sources and may range, for example, from between about 0.1% and 6.4%. The usual specification for gasoline up until a few years ago required that the total sulfur content be below 0.10%. In the past low sulfur crudes were plentiful and this specification could be met easily when using the simplest refining methods. There is, however, now insufficient low sulfur crude available to meet the demand and it is becoming necessary to process more and more crude petroleums having high sulfur contents. When processing such petroleums alone, it is impossible to meet the sulfur specification for gasoline without resorting to a specific desulfurization process. In view of this difficulty the Federal Government specification for total sulfur in gasoline was increased from 0.10% to 0.25%. Also in view of the importance of the problem a great deal of work was done in attempts to perfect a practical and efficient process for desulfurizing various oils. Some quite efficient hydrogenation processes have been developed. In these processes the sulfur compounds are broken up and the sulfur is removed in the form of hydrogen sulfide. These processes are, however, rather complicated, quite costly and have certain other drawbacks so that it is preferred not to apply them except where it becomes necessary. Other processes are known through which part of the sulfur compounds can be removed bodily from the oil. These processes are used in spite of the fact that they entail an appreciable loss of oil. This loss will be clear when it is considered that the sulfur is not present in the oil as such, but in the form of compounds. Thus, a sulfur content of, for example 1.0%, in a typical gas oil may mean that about 11% of the oil consists of undesirable sulfur compounds. The sulfur compounds removed bodily are of little value as such. They are usually burned in the airconia, boric oxide,- magnesia or the like. For

5 Claims. (01. me -32) disulfides so produced to the cracking zone.

further particulars regarding these catalysts, reference may be had to U. S. Patent No. 2,400,431.

When cracking sulfur bearing oils with catalysts of this type a certain amount of desulfuriz'ation is inherent. The desulfurization, however, is not complete and the gasoline contains appreciable amounts of sulfur, including sulfur in the form of mercaptans. The object of the present invention is to provide a method for the production of partially desulfurized gasoline from sulfur-bearing petroleum oils through catalytic cracking in which the sulfur is removed in the form of hydrogen sulfide and/or sulfur dioxide thereby avoiding loss of carbon values.

This object is accomplished according to the process of the present invention by cracking sulfur-bearing petroleum oils with a clay-type cracking catalyst whereby part of the sulfur is removed with the product gases as hydrogen sulfide and part of the sulfur is found in the gasoline as mercaptans, extracting the mercaptans from the cracked gasoline, oxidizing the extracted mercaptans to disulfides and cycling the In this method the sulfur-bearing oil is cracked simultaneously with the disulfides; the amount of hydrogen sulfide in the gases is increased; at the same time a gasoline free of mercaptans is produced without the loss of carbon values, since all of the sulfur removed is removed in the form of hydrogen sulfide and sulfur dioxide.

The process of the invention will be further described in connection with the attached schematic flow diagram. Referring to the flow diagram the oil to be cracked is fed to a conventional cracking unit I which may be of the fixed-bed type, moving-bed type, fluidized-bed type, or suspended-dust type, wherein it is cracked with a clay-type cracking catalyst. The preferred catalyst is one of the proprietary synthetic silica-alumina composite cracking catalysts, but other cracking catalysts of the clay type may also be used. The cracking is carried out at temperatures between 880 F. and 1100 F. to give an olefinic sulfur-bearing cracked gasoline. Any sulfur-bearing petroleum oil'boiling largely above the gasoline boiling range may be cracked but the process is best suited for the cracking of petroleum oilsrwhich are high in sulfur, i. e. containing 0.5% or more of sulfur.

The light hydrocarbon gases produced by the cracking are removed from the catalytic cracking' unit along with the hydrogen sulfide produced. The hydrogen sulfide is removed from the hydrocarbon product gases in the H28 removal unit 2. This unit may employ the Shell Phosphate Process (see The Refinery and Natural Gasoline Manufacture, issue of February 1941, page 116) or any one of the known competitive processes. The hydrogen sulfide may be recovered as such or it may be converted to elemental sulfur or sulfur dioxide if desired. The amount of sulfur thus removed will depend upon the throughput of the plant and the sulfur content of the feed but will, in a typical case, be in the order of 1,000 pounds per day.

The cracked gasoline, or a desired fraction of it, separated in the catalytic cracking unit from the gaseous products, higher boiling products and bottoms, is then passed to an extraction unit 3 wherein mercaptans are extracted. Any of the known methods for extracting mercaptans from gasoline may be employed. The usual and preferred method is to extract the gasoline with an immiscible solvent sufficiently alkaline to extract the mercaptans. Thus, for example, aqueous solutions of sodium hydroxide or potassium hydroxide may be employed. The extraction efficiency may be increased in the conventional manner by the presence of small amounts of so-called solutizers such as isobutyric acid, alkyl phenols, or the like. One suitable process for the extraction of the mercaptans is, for

example, the Solutizer Process described in the Oil and Gas Journal, issue of July 18, 1940, pages 36-40. Variations of this process as well as other known processes can however also be used. The gasoline substantially freed from mercaptans is withdrawn via line 4.

The mercaptans are then oxidized to disulfides in an oxidizer. This is preferably eifected by bubbling air through them in the presence of an oxidation catalyst such for instance as tannin or an alkaline solution of picramic acid. Thus, for example, air may be blown up through the mercaptans at room tempearture or a temperature slightly above room temperature up to about 150 F. in the presence of a caustic solution containing a small amount of picramic acid. The disulfides which are relatively insoluble tend to separate. They may, if desired, be withdrawn as such. A better separation may however be obtained by taking them up in a hydrocarbon oil. A wash oil for this purpose may be introduced via line 6. Any hydrocarbon oil may be used for this purpose. Thus, for example, a naphtha fraction or a kerosene fraction may be advantageously used. The wash oil and the disulfides are then passed via line i to the cata lytic cracking unit wherein the disulfides are cracked along with the sulfur-bearing feed stock. The disulfides, it is found, crack easily and substantially completely under the cracking conditions used to produce further quantities of hydrogen sulfide. Thus, when cracking a gas oil with a synthetic silica-alumina cracking catalyst at a temperature of 1000 F., the sulfur introduced in this method as disulfides has been found to distribute itself approximately as follows:

Thus, the sulfur is substantially all removed in the form of hydrogen sulfide and sulfur dioxide 4 and that which is removed, is removed without any appreciable loss of carbon values. If the petroleum oil feed contains a very high concentration of sulfur the gasoline product may still contain more sulfur than is allowed by the specification (in the form of thiophenic sulfur compounds which cannot be removed with extraction by alkali). In such cases it may be desirable to treat a portion of the catalytically cracked gasoline by a different method to remove some of the thiophenic sulfur. This is preferably done by subjecting part of the gasoline to a hydrogenation treatment in a hydrogenation unit 8. The hydrogenated gasoline may then be blended with that produced with the method of the invention. Where it is necessary or desirable to hydrogenate part of the gasoline it is best to first separate the catalytically cracked gasoline into two fractions boiling below and above about 220 F. The lower boiling fraction is then treated according to the method of the invention and the higher boiling fraction is subjected to the hydrogenation treatment. The treatment with hydrogen to remove more resistant sulfur compounds can, if desired, be applied to part of the gasoline product obtained by method of the invention, instead of a portion of the raw cracked gasoline. Since the d-esulfurization by hydrogenation is an optional treatment which can advantageously be applied to a part or fraction of the cracked gasoline in cases where large amounts of refractory sulfur compounds are present this treatment has been indicated in the flow diagram by dotted lines.

The invention is defined in the following claims:

1. A process for the production of partially desulfurized gasoline which comprises cracking a petroleum oil containing at least 0.5% sulfur in a cracking zone with the aid of a clay-type cracking catalyst thereby to produce a gaseous product containing hydrogen sulfide and a mercaptancontaining hydrocarbon fraction boiling in the gasoline boiling range, extracting mercaptans from said fraction with an immiscible alkaline solvent, oxidizing the mercaptans so extracted to disulfides, and passing said disulfides to said cracking zone whereby the disulfides are cracked simultaneously with said first-mentioned sulfurbearing petroleum oil with the formation of further quantities of hydrogen sulfide.

2. A process for the production of partially desulfurized gasoline which comprises cracking a petroleum oil containing at least 0.5% sulfur in a cracking zone with the aid of a clay-type cracking catalyst thereby to produce a gaseous product containing hydrogen sulfide and a mercaptancontaining hydrocarbon fraction boiling in the gasoline boiling range, extracting mercaptans from said fraction with an immiscible alkaline solvent, oxidizing the mercaptans so extracted to disulfides, dissolving the disulfides so formed in a hydrocarbon oil and passing said hydrocarbon oil containing the disulfides to said cracking zone whereby the disulfides are cracked simultaneously with said first-mentioned sulfur-bearing petroleum oil with the formation of further quantitles of hydrogen sulfide.

3. A process for the production of partially desulfurized gasoline which comprises cracking a petroleum oil containing at least 0.5% sulfur in a cracking zone with the aid of a clay-type cracking catalyst thereby to produce a gaseous product containing hydrogen sulfide and a merc'aptancontaining hydrocarbon fraction boiling in the gasoline boiling range, extracting mercaptans from said fraction with an aqueous caustic alkali solution, oxidizing the mercaptans so extracted to disulfides, dissolving the disulfides so formed in a hydrocarbon oil and passing said hydrocarbon oil containing the disulfides to said cracking zone whereby the disulfides are cracked simultaneously with said first-mentioned sulfur-bearing petroleum oil with th formation of further quantities of hydrogen sulfide.

4. A process for the production of partially desulfurized gasoline which comprises cracking a petroleum oil containing at least 0.5% sulfur in a cracking zone with the aid of a synthetic silicaalumina composite cracking catalyst thereby to produce a gaseous product containing hydrogen sulfide and a mercaptan-containing hydrocarbon fraction boiling in the gasoline boiling range, extracting mercaptans from said fraction with an immiscible alkaline solvent, oxidizing the mercaptans so extracted to disulfides, and passing said disulfides to said cracking zone whereby the disulfides are cracked simultaneously with said first-mentioned sulfur-bearing petroleum oil with the formation of further quantities of hydrogen sulfide.

5. Process for the production of partially desulfurized gasoline which comprises cracking a petroleum oil containing at least 0.5% sulfur in a cracking zone with the aid of a clay-type cracking catalyst thereby to produce a gaseous product containing hydrogen sulfide and a mercaptan- 1 containing hydrocarbon fraction boiling in the REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,998,863 Chaney et a1 Apr. 23, 1935 2,151,721 Schulze Mar. 28, 1939 2,324,927 Heilman July 20, 1943 2,336,174 Hewlett Dec. 7, 1943 2,337,003 Schulze Dec. 14, 1943 2,352,059 Woog June 20, 1944 2,415,477 Folkins et a1. Feb. 11, 1947 2,450,724 Grote Oct. 5, 1948 

1. A PROCESS FOR THE PRODUCTION OF PARTIALLY DESULFURIZED GASOLINE WHICH COMPRISES CRACKING A PETROLEUM OIL CONTAINING AT LEAST 0.5% SULFUR IN A CRACKING ZONE WITH THE AID OF A CLAY-TYPE CRACKING CATALYST THEREBY TO PRODUCE A GASIOUS PRODUCT CONTAINING HYDROGEN SULFIDE AND A MERCAPTANCONTAINING HYDROCARBON FRACTION BOILING IN THE GASOLINE BOILING RANGE, EXTRACTING MERCAPTANS FROM SAID FRACTION WITH AN IMMISCIBLE ALKALINE SOLVENT, OXIDIZING THE MERCAPTANS SO EXTRACTED TO DISULFIDES, AND PASSING SAID DISULFIDES TO SAID CRACKING ZONE WHEREBY THE DISULFIDES ARE CRACKED SIMULTANEOUSLY WITH SAID FIRST-MENTIONED SULFURBEARING PETROLEUM OIL WITH THE FORMATION OF FURTHER QUANTITIES OF HYDROGEN SULFIDE. 